1. Field of the Invention
The present invention relates to stamp devices employing stencil paper such as heat sensitive stencil paper capable of being perforated by infrared irradiation or heat provided by a thermal head, and more particularly to compact portable stamp devices which can be used in varying environmental conditions.
2. Description of Related Art
A compact portable stamp device which employs stencil paper having a perforated pattern of characters, figures, etc. formed by using a pencil or a ball-point pen is known. For example, FIG. 17 shows a stamp device disclosed in U.S. Pat. No. 3,799,053. The construction of the stamp device will be explained with reference to FIG. 17.
The stamp device includes a table 100, a bottle grip 101, an inking unit 102, a compression spring 103 and a syphon tube 105. The bottle grip 101 is flexible and is used like a squeeze bottle. That is, the inside of the bottle grip 101 is hollow, with liquid ink stored therein.
Compression spring 103 is disposed between bottle grip 101 and table 100. Compression spring 103 presses bottle grip 101 and table 100 so as to part them from each other. Therefore, inking unit 102 connected to bottle grip 101 is usually arranged within the confines of table 100. Therefore, even if the table 100 is placed on a medium to be printed, such as ordinary plain paper, the medium does not receive a printing image.
Table 100 is made from a metal plate, such as aluminum, so as to be easily cleaned. The four sides of the metal plate are bent downwardly so that the lower side of table 100 is open. An aperture is formed at the center of the upper side of table 100. Bottle grip 101 and the inking unit 102 are connected to each other through the aperture.
An ink pad is disposed inside of inking unit 102, such that the liquid ink stored in bottle grip 101 will be supplied to the ink pad. A stencil paper 104 having a perforation pattern of characters, figures, etc. formed by using a pencil a ball-point pen or other pointed instruments is detachably arranged under the ink pad.
Syphon tube 105 is provided in bottle grip 105 and supplies the ink stored in bottle grip 101 to the ink pad of inking unit 102.
Next, the operation of the stamp device will be explained with reference to FIG. 17. In the stamp device, a user draws characters, figures, etc. on stencil paper 104 by using a pencil or a ball-point pen. Stencil paper 104 is then perforated based on the drawn pattern. Next, the user installs stencil paper 104 under inking unit 102 and places the stamp device on a medium to be printed, such as ordinary paper. The user grasps bottle grip 101 and pushes it downward. This causes inking unit 102 to descend against the bias of compression spring 103, so that inking unit 102 is pressed against the ordinary paper through stencil paper 104. Ink from the ink pad of inking unit 102 then passes through the perforations of stencil paper 104 so that the ordinary paper is printed with the ink in the pattern formed on stencil paper 104. If the user stops pressing down on bottle grip 101, the stamp device returns to the former state by expansion of compression spring 103 so that the inking unit 102 parts from the ordinary paper, completing the printing operation.
If after a plurality of print operations, the ink of the ink pad is depleted, the user firmly grips and squeezes flexible bottle grip 101. This causes the ink in bottle grip 101 to pass through syphon tube 105 and be supplied to the ink pad of inking unit 102.
Heat sensitive stencil paper which can be perforated by infrared irradiation or heat provided by a thermal head is also known. A typical example of such heat sensitive stencil paper is formed by bonding a thermoplastic film and a porous thin paper to each other by use of an adhesive. FIG. 18 shows a compact portable stamp device employing such heat sensitive stencil paper disclosed in Japanese Laid-Open Patent No. Sho 63-17074. Heat sensitive paper is also disclosed in the above-incorporated U.S. patent application Ser. No. 07/812,107.
The stamp device of FIG. 18 employs a mimeograph printing plate 106. Mimeograph printing plate 106 consists of perforated heat sensitive stencil paper 110, an ink impermeable cover sheet 112 and a frame 108. The frame 108 has a central aperture. Heat sensitive stencil paper 110 to be perforated by infrared irradiation or heat from a thermal head is installed under frame 108. Ink impermeable cover sheet 112 is installed on the other side of frame 108. The mimeograph printing plate 106 can be filled with ink between heat sensitive stencil paper 110 and ink impermeable cover sheet 112. The main body 130 of the stamp device comprises a base 114, a cushion layer 116, a cohesive layer 118 and a grip member 120 fixed to base 114.
Base 114 is a rigid member such as synthetic resin or wood. Cushion layer 116 is a foam body such as urethane or sponge, and has a hexahedron shape. Cushion layer 116 is bonded under the base 114 by an adhesive.
Cohesive layer 118 is a gel silicon rubber, a rubber with moderate adhesion such as monomer residual polyurethane rubber, or other rubber-like materials. Cohesive layer 118 can be adhered to cover sheet 112 of mimeograph printing plate 1 06. The base shape or base area of cohesive layer 118 is almost the same as that of the aperture formed in the center of frame 108. Cohesive layer 118 is bonded to cushion layer 116 by adhesive.
Next, the operation of the stamp device will be explained with reference to FIG. 18. Heat sensitive stencil paper 110 of mimeograph printing plate 106 is perforated by infrared irradiation or heat provided by a thermal head (not shown) so as to have a perforation pattern of characters and figures therein. Next, the user places ink on heat sensitive stencil paper 110 while cover sheet 112 is turned up from frame 108 (as shown in FIG. 18). Because a porous thin paper layer of the heat sensitive stencil paper 110 faces the inside of frame 108, the ink is maintained within frame 8 by the porous thin paper layer. Next, the user closes cover sheet 112. The user then places main body 130 and mimeograph printing plate 106 together such that the cohesive layer 118 of main body 130 is attached into the aperture of frame 108. The user then places main body 130 to which mimeograph printing plate 106 is fixed, onto the medium to be printed. Next, the user grasps grip member 120 and pushes it downward. The ink between heat sensitive stencil paper 110 and cover sheet 112 is pressed through the porous thin paper layer of sheet 110, and passes through each perforation in heat sensitive stencil paper 110 so that the ink adheres onto the medium to be printed.
If after a plurality of print operations the ink between heat sensitive stencil paper 110 and cover sheet 112 is depleted, the user removes main body 130 from mimeograph printing plate 106, and places additional ink onto heat sensitive stencil paper 110 while cover sheet 112 is turned up from frame 108. Afterwards, the user closes the cover sheet 112 as described above, and places main body 130 and mimeograph printing plate 106 together such that cohesive layer 118 of main body 130 is attached into the aperture of frame 108. Thus, the print operation can be executed again.
In the above-described conventional stamp device, the viscosity of the ink is dependent on an environmental temperature of the stamp device. (Specifically, the temperature of ink in the stamp device which is usually about the same as the temperature of the environment in which the stamp device is used.) Therefore, there is a problem that the print quality is influenced directly by changes in environmental temperature.
This problem will be explained with reference to FIG. 9, FIG. 15 and FIG. 16. FIG. 9 shows the letter "I" printed by using a stamp device. FIG. 15 is an enlarged view showing the printing of individual spots which comprise the FIG. 9 print at a low environmental temperature. FIG. 16 is an enlarged view showing the printing of individual spots at a high environmental temperature.
When the environmental temperature is low, the viscosity of the ink becomes high (i.e., the ink thickens). Therefore, the high viscosity of the ink produces an ink printing state as illustrated in FIG. 15. The individual spots are spaced far apart from each other resulting in less clear characters. When the environmental temperature is high, the viscosity of the ink becomes low (i.e., the ink runs more easily). Therefore, the low viscosity of the ink causes the ink spots to overlap at, for example, overlapped portion 62 as shown in FIG. 16. This also adversely affects the resulting character.
As described above, there is a problem in that printing reproducibility is deteriorated due to the environmental temperature of and around the stamp device even if the perforations can be formed to have substantially the same diameter.